Apparatus for the production of stretched wire

ABSTRACT

A stretching machine ( 21 ) for the production of discontinuously stretched wire ( 31 ) comprises a rolltype straightening mill ( 22 ), a first roll-type advancing unit ( 23 ), a first clamping device ( 24 ), which is capable of being moved on a hydraulic linear booster ( 25 ), and a second clamping device ( 28 ), to which a cutting device ( 29 ) is attached. A pushed-in rolled wire ( 31 ) to be stretched is prestraightened by the roll-type straightening mill ( 22 ) and is advanced to the second clamping device ( 28 ) by the first rolltype advancing unit ( 23 ). Subsequently, the wire ( 31 ) is held by the two clamping devices ( 24  and  28 ), the first clamping device ( 24 ) being moved opposite to the push-in direction by the amount of a degree of stretching and correspondingly cold-forming the rolled wire. By means of the apparatus, a favourable yield-point ratio is achieved, the strain properties being maintained. By means of a sensor, the final values of, for example, the steel stress are detected, stored and used for the further production of the stretched wires.

TECHNICAL FIELD

[0001] The invention relates to an apparatus for the production ofdiscontinuously stretched wire, with two spaced-apart clamping devices,at least one of which is capable of being moved by the amount of astretching length. Further, a plant with such an apparatus preceding itis claimed. In addition, the invention relates to methods for theindustrial production of discontinuously stretched wire.

PRIOR ART

[0002] For structural-steel mats—what are known as reinforcingmeshes—cold-rolled steel wire (KR) is mainly used, which is rolled inthe incandescent state in the steel mill and is subsequently cold-formedto the desired nominal dimension and ribbed in two stages on acold-rolling plant. For embossing the ribs, the wire is formed by theamount of 15% to 25%. Cold-formed wires have increased strength, ascompared with a rolled wire, but at the same time the material becomesmore brittle and the elasticity falls.

[0003] The most important characteristic quantities for structural steeland, in particular, for wires in structural-steel mats arepredetermined, for example, by the German DIN standard 488. Thepresent-day steel qualities for structural steel consist 100% of scrap,primarily of scrap from motor vehicles, and contain sometimes highalloying fractions of various foreign metals. As a result, the minimumvalues, required in the standards, for the yield point (R_(e)) and thetensile strength (R_(m)) are achieved without any particular outlay.Cold-forming for producing the ribs is no longer required in order toachieve the prescribed strengths. However, it becomes increasingly moredifficult to meet the requirements as to the yield-point ratio(R_(m)/R_(e)) and the elasticity properties.

[0004] Hot-rolled and ribbed steel wire (WR) is rolled in theincandescent state to the nominal dimension. In the last rolled stand, aribbing is applied to the rolled wire. So that the yield point (R_(e))reaches a higher value than is normally afforded in the case of a WR,the WR may be cold-formed in an additional work step. For example, theWR is cold-formed by stretching.

[0005] At the present time, three basic types of stretching are employedin practice and can be divided into two main groups. The first maingroup constitutes continuous stretching, in this case a multiaxial oruniaxial stress being exerted on the wire. Continuous stretching withmultiaxial stress is the method adopted most frequently for theproduction of stretched wire. The wire is drawn through upper and lowerrolls which are displaced relative to one another in their axialorientation in such a way that the wire is drawn through these rolls ina serpentine manner. Combination plants, which combine the cold-rollingand stretching operations, are often used for this purpose. In the othermethod of continuous stretching, a uniaxial stress is applied to thewire. The wire is led around a first roll in the opposite direction andagain in the drawing direction over a second roll which is arranged inthe opposite direction to the tensile force with respect to the firstroll. In the view of the rolls, the wire is led in the form of ahorizontal 8. This method for the production of stretched wire is hardlyused nowadays because of the high outlay in mechanical terms and thelack of flexibility.

[0006] A further possibility for discontinuous stretching with uniaxialstress belongs to the second main group. In this method, the wire isstretched, straightened and cut in a combined manner. Due to what may bereferred to as the start/stop mode of operation, this method isappreciably slower than continuous methods.

PRESENTATION OF THE INVENTION

[0007] The object of the invention is to provide an apparatus and theassociated method which allows a discontinuous stretching of wire athigh speeds and with high production reliability.

[0008] The solution for achieving the object is defined by the featuresof claim 1. According to the invention, an apparatus for the industrialproduction of discontinuously stretched wire has two spaced-apartclamping devices, at least one of which is capable of being moved by theamount of a return stroke and at least one of which is equipped with asensor for determining the wire stress.

[0009] By industrial production is meant production in quantities. Thisis in contrast to test arrangements, in which individual wires aremachined and processed in order to arrive at test results, for examplein a destructive test for checking the maximum tensile strength.

[0010] The wire is delivered as a rolled-wire bundle in the form of acoil. By means of the one clamping device capable of being moved by theamount of the stretching length, during stretching the wire issimultaneously straightened by virtue of plastic deformation. There isno need for any additional setting work, as in the case of straighteningblades or roll-type straightening mills. Further, the wire stress isdetected continuously by means of the sensor. The detected values may bestored, assigned to a wire portion. Wire portions produced thereafterare checked merely with regard to their final values. Stretching canautomatically be adapted continuously on the basis of statisticevaluations of the measured values. In addition, a stress thresholdvalue may be predetermined, at which the wire portion to be stretched isoriented absolutely straight.

[0011] The degree of stretching can thus be programmed continuously.Adaptations on the apparatus when different production lengths are to beproduced may therefore be dispensed with. Further, in the event of achange in the diameter of the wire, the apparatus does not have to beconverted.

[0012] Each wire portion is checked continuously by means of the valuesdetected by the sensor and stored. Material strength fluctuations aredetected during production, and the apparatus can be adaptedcontinuously, according to the detected values, to the material to beprocessed. At the same time, any material faults or rejects are detectedby the apparatus during production, and wires of lower quality can beseparated out or be removed from the further process for the productionof finished products. This prevents the situation where wire portions oflower quality are welded together with wire portions conforming to thestandards in order to form structural-steel mats. Any rejects whichthere may be are merely individual wire portions, not entirestructural-steel mats. This leads not only to a material saving, butalso to an appreciable time saving in the production of structural-steelmats.

[0013] Preferably, means for introducing or advancing the wire in thewire longitudinal direction are provided. As is typical of industrialproduction, the rolled wire is introduced directly from the rolled-wirebundle into the apparatus according to the invention. In this case, therolled wire may be shot into the apparatus. The means for introducing oradvancing the wire ensures the feed during production, even when achange of the rolled-wire bundle takes place.

[0014] In a variant of this, cut-to-length and preferablyprestraightened wire portions can preferably be fed from a magazine orstorage unit of the apparatus according to the invention transversely tothe stretching direction. The wire portions fed in this way arestretched to the apparatus and are subsequently further processed.

[0015] On the entry side, the apparatus is preferably provided with aroll-type straightening mill. The latter prestraightens the wire to anextent such that it can be pushed through the apparatus more easily.Preferably, the rolls of the roll-type straightening mill are mounteddisplaceably, so that the distance between the rolls arranged above andbelow is adapted to the diameter of the wire preferably by automaticcontrol. For an automatic control of the rolls of the roll-typestraightening mill, for example, the first mutually opposite rolls inthe push-in direction can be mounted so as to be freely moveable. Whenthe wire is introduced, the rolls are displaced out of their neutralposition respectively upwards and downwards according to the diameter ofthe wire. By means of a separate sensor, the distance between the firsttwo rolls can be detected and the following rolls can be positioned bymechanical control according to this distance. Further, a spring forcecan act on the displaceable rolls, which exerts on the wire asufficiently high pressure force for the satisfactory guidance of thewire.

[0016] Instead of a roll-type straightening mill, the wire may be bentstraight, for example by straightening pressing. Another possibility forprestraightening the wire is a straightening rotor with straighteningblocks. Further, the apparatus according to the invention may bepreceded by a flat-straightening machine which orients the wire,straight, prior to the stretching. Furthermore, the roll-typestraightening mill may be replaced essentially by any apparatus which,for example, at least prestraightens the wire by rolling, drawing orpressing.

[0017] Preferably, in the apparatus, a first roll-type advancing unit, afirst clamping device, a straightening section and a second clampingdevice are arranged downstream of the roll-type straightening mill inthe direction of advance of the wire. The approximately prestraightenedwire is led, by means of the first roll-type advancing unit, out of theroll-type straightening mill and through the first clamping device, thestraightening section and the second clamping device. After the twoclamping devices retain the wire, the wire is stretched by the at leastone moveable clamping device, preferably the first clamping device. Bymeans of the roll-type advancing unit, the wire is transported furtheron, so that the operation can be repeated for the next wire portion.

[0018] In a variant of this, the first roll-type advancing unit may bearranged downstream of the first clamping device in the direction ofadvance of the wire, the roll-type advancing unit coming to rest withinthe straightening section. Further, only the second clamping device maybe capable of being moved. Further, both, the first and the second,clamping devices may be designed to be moveable.

[0019] The straightening section preferably has an adaptable length. Forthis purpose, for example, the roll-type straightening mill, the firstroll-type advancing unit and the first clamping device are combined toform a unit of the apparatus, and the second clamping device is designedas a further unit of the apparatus which is displaceable relative to thefirst unit. The second unit may be shortened, for example by means of aworm drive, from a predetermined maximum length of the straighteningsection to any desired dimension. The maximum length of thestraightening section is in interrelation with the length of travel ofthe moveable clamping device, the said travel resulting from the degreeof stretching.

[0020] In order to simplify the wire transport during the entireproduction, a second roll-type advancing unit, which assists the wiretransport, may be arranged upstream of the second clamping devicebetween the straightening section and the second clamping device. Thearrangement of the second roll-type advancing unit may be advantageousparticularly in the case of high numbers of cycles of the apparatus. Asregards the arrangement of two roll-type advancing units, these arepreferably operated synchronously. In a variant, for example, only oneof the roll-type advancing units is actively operated and the otherroll-type advancing unit corotates passively. The wire can be maintainedunder prestress by means of the second roll-type advancing unit.

[0021] The first clamping device, which is arranged on the entry sideand is capable of being moved by the amount of the stretching length, ispreferably arranged on a linear hydraulic power booster which canexecute freely programmable travels. A rolled wire is stretchedpreferably by the amount of 3% to 5% in the apparatus according to theinvention. The necessary stroke or the executable travel of the firstclamping device thus amounts to somewhat more than 5% of the length ofthe maximum straightening section. Instead of the moveable clampingdevice on a hydraulic power booster, another tensioning device may alsobe provided.

[0022] Alternatively to this, the second clamping device may be arrangedon a linear hydraulic power booster, in this variant the first clampingdevice arranged on the entry side being arranged fixedly. Further, bothclamping devices may be arranged on linear hydraulic power boosters. Insuch an arrangement, the clamping devices are moved preferablysimultaneously away from one another or alternately in oppositedirections until the rolled wire has been lengthened by the amount ofthe desired stretching dimension.

[0023] Preferably, a pressure cell is arranged as a sensor on the fixedclamping device. By means of the pressure cell, the stress in the wireduring the entire stretching operation and, in particular, the finalvalue for each stretched wire portion is detected. The pressure cell mayoperate, for example, on the basis of a spring (spring principle) or onthe basis of hydraulic pressure (hydraulic principle). The data from thepressure cell are stored in a control unit and are made available forthe further production of stretched wire. Discontinuous stretching withsimultaneous (online) quality control is made possible by means of themeasured and stored values.

[0024] The stored final values may be used further for statisticevaluation for the individual stretched wire portions. A stressthreshold value may also be defined, which lies unquestionably on theelastic straight line of the stress/strain diagram of the rolled wire,thus ensuring that the wire is oriented absolutely straight and thatstretching has commenced.

[0025] Further, the apparatus preferably has a cutting unit arranged onthe exit side, in order to cut the stretched wire to length. Preferably,the stretched wire is cut to the desired length by means of a cuttingdevice, for example a shear arrangement. As a variant of this, thestretched wire may also be cut to length by means of a cutting torch.

[0026] For receiving the cut-to-length wires, a receptacle is preferablyarranged at the exit of the apparatus according to the invention, thesaid receptacle preventing the cut-to-length wires from falling to theground and making the wires available for further processing. If theapparatus is preceded by a wire-mesh welding machine, the receptacleserves as a material repository or storage region, from which the wiresrequired are extracted by a feed device of the wire-mesh weldingmachine.

[0027] Preferably, the apparatus comprises a control device which setsthe stretching length on the basis of the wire stress measured by thesensor. If the total length of the wire portion to be stretched amountsto more than the length of the straightening section, which isdetermined by the distance between the first and the second clampingdevice, in a first step the wire portion is lengthened by the amount ofthe maximum possible stretching length which is in a percentage relationto the straightening section. Subsequently, the wire is advanced by themissing amount of the desired total length and is stretched once again,in the same percentage relation, by an amount which results from theamount of the advance. Preferably, the stretching length isautomatically adapted, by means of the control, to the length of thestraightening section or of the advance.

[0028] The control is typically designed as a module and is notinstalled permanently in the apparatus. It is thereby possible for thecontrol to be employed, adapted according to the user's requirements orto the local conditions.

[0029] Advantageously, a plant with a wire-mesh welding machine ispreceded by an apparatus according to the invention for the productionof discontinuously stretched wire. Thus, the stretched and cut-to-lengthwire portions are made available directly to the wire-mesh weldingmachine for further processing and can be taken over from a wire feeddevice of the wire-mesh welding machine.

[0030] In this case, for example, two apparatuses according to theinvention for the production of discontinuously stretched wire mayprecede a plant having a wire-mesh welding machine. One of theapparatuses according to the invention produces the transverse wires andthe other apparatus produces the longitudinal wires. The stretched wiresrequired is [sic] extracted from the corresponding intermediate stores,for example by means of two feed devices of the wire-mesh weldingmachine, and is [sic] positioned for further processing. By means ofsuch an arrangement, the production times and production costs arelowered decisively, since the components of the two apparatuses and thestretching length can be coordinated with the maximum dimensions of thedesired transverse and longitudinal wires, while at the same time a highquality of the stretched transverse and longitudinal wires is ensured.

[0031] In the method for the industrial production of discontinuouslystretched wire, a wire portion to be machined is gripped by two clampingdevices and is stretched. By means of a sensor for measuring the wirestress and of a travel sensor, a stress/strain dependence is recorded.This is stored, assigned to the wire portion, for further processing. Ina first step, a new wire is stretched in what may be referred to as astart/stop operating mode, and the stress/strain dependence for thisspecific wire portion is recorded. Subsequently, the stretching of thefurther wire portions commences, with the apparatus at full capacity,and only the final values of each individual wire portion are checked.If a measured final value of a stretched wire portion lies outside apredefined tolerance range, the apparatus can be adapted correspondinglyor the wire portion having the values lying outside the tolerance isseparated out. As a result of this online quality control, productionreliability is ensured during the entire production of the wire portionsand is improved, as compared with the known methods for a discontinuousstretching of wire portions, and also the quantity of rejects isreduced. There are no wire portions of lower quality welded togetherwith wire portions conforming to the standards, to form structural-steelmats, thus preventing the situation where entire structural-steel matshave to be discarded. This leads not only to a material saving, but alsoto an appreciable time saving in the production of structural-steelmats.

[0032] The method has the advantage that work can be carried out withhigh numbers of cycles and, compared with previous methods, productionreliability is improved. If stretching is regulated by the tensileforce, only stretching with low numbers of cycles is possible, since theforce changes discontinuously from the commencement of stretching to thedesired stretching length. At the same time, the stored values can beprinted out for each rolled-wire bundle and also for each wire portion.This print-out may serve as a certificate of quality for the material ofstructural-steel mats. If the wires are sold on as semi-finishedproducts, the printed-out list or a copy of this may be enclosed as aquality voucher with the wire bundle. A quality control is provided,which satisfies any ISO standard and makes it possible to have reliableevidence of rod production.

[0033] In a further method for the industrial production ofdiscontinuously stretched wire, the stretching length for a wire portionis automatically adapted continuously on the basis of statisticevaluations of the stress/strain dependence. Automatic adaptation takesplace, for example, via the travel and/or the force. If the steelquality changes or a new rolled wire is introduced into the apparatus,the machine is adapted automatically. By means of this method,operational documentation can be prepared from the production of thewire portions and may be used, on the one hand, for operating-dataacquisition and, on the other hand, for quality assurance.

[0034] In another method for the industrial production ofdiscontinuously stretched wire, the stretching length for a wire portionis related to a stress threshold value which defines the conclusion of apreflattening phase. In terms of the stress/strain diagram of the rolledwire, a value is defined as a control point on the elastic straightline, the said value ensuring that the wire portion is absolutelystraight. First, the wire is flattened. The end of the “gradation phase”can be determined by means of the stress threshold value. A rolled wiredelivered as a bundle must first be oriented absolutely straight, sothat stretching is carried out in the required size and quality. As soonas the sensor detects that the wire is absolutely straight even at alower value, where appropriate the stress threshold value can be reducedfor the subsequent wire portions.

[0035] Preferably, the stress threshold value is determined individuallyfor each wire portion. The sensor detects when the wire is in anabsolutely straight position and the applied force is used solely forstretching and no longer straightens the wire.

[0036] Typically, in all the methods, the wire is introducedautomatically in the wire longitudinal direction and is cut to lengthautomatically after stretching.

[0037] Further advantageous embodiments and feature combinations of theinvention may be gathered from the following detailed description andfrom the whole of the patent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In the drawings used for explaining the exemplary embodiment:

[0039]FIG. 1 shows a stress/strain diagram for a hot-rolled and ribbedwire (WR) in the rolled and stretched state; and

[0040]FIG. 2 shows an exemplary arrangement of a stretching machineaccording to the invention.

[0041] Identical parts are basically given the same reference symbols inthe figures.

WAYS OF IMPLEMENTING THE INVENTION

[0042]FIG. 1 illustrates a stress/strain diagram for a hot-rolled andribbed wire (WR) in the rolled and stretched state. The strain ε isplotted on the abcissa axis 2 of the diagram 1 and the stress C isplotted on the ordinate axis 3. The curve 4 illustrates thecharacteristic curve of a naturally hard steel—here a rolled wire—In thestress/strain diagram. The wire is drawn and reaches its yield pointR_(e). Up to this point, the steel is in its elastic range and wouldresume its original length if the tensile force were removed. Beyond theyield point R_(e), under a further action of force, the steel begins toflow (what is known as the flow plateau) . At the end of the flowplateau 5, the stress in the steel rises further from the end of theflow plateau 5 to the maximum tensile strength R_(m) (here alsodesignated as the point 6). The region 7 from the zero point to theyield point Re is designated as elastic strain. The region 8 from theyield point Re to the tensile strength R_(m) (point 6) is designated asthe plastic strain. If, after the tensile strength R_(m) is reached,further tensile force is exerted on the steel, the stress σ falls andthe steel begins to contract at its weakest point until it breaks. As aresult of the stretching, the wire is extended into the range of plasticstrain (for example up to the point 9). The strain ε of the wire is inthis case normally in the range from 3% to 5%. The wire was cold-formedby stretching.

[0043] As soon as the stretched wire portion is relieved of stress, thewire portion is minimally shortened, as illustrated by the point 10. Ifthe stretched wire is loaded once again, the steel behaves essentiallythe same way as a cold-formed wire on which the ribs and also thereduction in diameter due to elongation have been produced bycold-forming. In contrast to this, however, the stretched WR has betterstrain properties than a ribbed KR. As a result of the stretching, theWR has a new yield point R_(er) which, in terms of the value of thestress σ, is nearer (by the difference between the yield point R_(e) andthe yield point R_(er)) to the tensile strength R_(m) than in the caseof a non-stretched wire. The wire behaves elastically again in theregion 11 and plastically in the region 12. A preferred yield-pointratio is achieved by means of the stretching, the better strainproperties of the rolled wire being essentially maintained.

[0044] On the apparatus according to the invention, mainly wire fromrolled-wire bundles in the form of coils is used. The wire introducedinto the apparatus is not oriented absolutely straight. Consequently, atthe commencement of the application of stress, the characteristicdiagram, as illustrated by the curve 4, is not obtained. Until the wireis oriented absolutely straight, a discontinuous curve 13 is obtained.The actual stretching of the wire commences from the intersection point14 of the curve 13 with the elastic straight line 15 of the curve 4. Astress threshold value 16 can therefore be defined, which either isdetermined individually for each wire portion to be stretched or isdetermined as a fixed value. As soon as, for example, a pressure cellmeasures the stress threshold value, there is the certainty that thepreflattening phase is concluded and actual stretching commences. Thestress threshold value 16 amounts, for example, to 200 N/mm², whichcorresponds approximately to one third of the yield point Re of the wirematerial. This stress threshold value 16 may be set even higher in thecase of sharply bent wire material, in which case the value of thestress threshold value 16 should lie preferably clearly below the valueof the yield point Re (<500 N/mm²)

[0045] By means of the sensors, all the values can be recorded and areavailable to the control, on the one hand, for preparing a stress/straindependence which is stored, assigned to the wire portion, for furtherprocessing. On the other hand, the measured values may be used forcontinuously automatic adaptation of the stretching length on the basisof the statistic evaluation of the stress/strain dependence. Further,the stored values may be printed out and used for operational and/orquality documentation. Further, by means of the stored values, thevarious phases can be determined computationally from the characteristiccurve 4.

[0046] An exemplary arrangement of a stretching machine according to theinvention is shown in FIG. 2. The stretching machine 21 comprises on theentry side (on the left in relation to the drawing) a roll-typestraightening mill 22 which is followed by a first roll-type advancingunit 23. There then follows a first clamping device 24 arranged on ahydraulic linear booster 25, on which the first clamping device 24 iscapable of being moved horizontally in a controlled manner. Thesecomponents form a first part 26 of the stretching machine 21. A secondpart 27 is formed by a second clamping device 28 which comprises acutting device 29. The second part 27 may comprise, further, a secondroll-type advancing unit. By means of the second roll-type advancingunit, for example, the wire 31 can be maintained under prestress, or thesaid unit serves for assisting the first roll-type advancing unit 23during the advance of the wire 31.

[0047] The length of the straightening section 32 may be varied, asrequired, by the stretching machine 21 being divided into a first part26 and a second part 27 which are capable of being moved relative to oneanother by means of a separate device (not illustrated here) . In orderto move the two parts relative to one another, for example, the firstpart 26 may be mounted fixedly on a stand and the second part 27 may befixed, for example, on a worm gear which is operated by means of amotor. The length of the straightening section 32 can consequently beadapted to the production requirements. The straightening section 32 isformed, for example, by a stable steel girder (for example, a U-profile,such as a UNP or UAP) . So that the straightening section 32 can beadapted in its length, for example, two U-profiles are arranged, whichare capable of being pushed one into the other and which overlap oneanother according to the set length. In a variant, the second part 27may be provided with a recess or be designed in such a way that thesteel girder of the straightening section 32 passes through the saidsecond part when the length of the straightening section 32 is shortenedby the second part 27 being moved.

[0048] The straightening section 32 begins at the first clamping device24 and ends at the second clamping device 28. The maximum straighteningsection 32 may be designed according to the user's wishes orrequirements, the maximum stroke of the hydraulic linear booster 25having to be taken into account. If, for example, the length of thestraightening section is 4000 mm and the usual degree of stretching of3% to 5% is to be carried out, the stroke of the moveable first clampingdevice 24 must amount to at least 200 mm. If the straightening section32 is increased, for example, to 8000 mm, the stroke of the moveablefirst clamping device 24 would therefore have to amount to at least 400mm according to the length of the straightening section 32. With themeans available at the present time, the length of the straighteningsection 32 is expediently to be limited to below 5000 mm for structuralreasons and with a view to the production costs and also on grounds ofthe serviceability of the stretching machine 21.

[0049] If, for example, a wire portion having, for example, a length of6000 mm is to be produced on a stretching machine 21 with a maximumstraightening section 32 of 4000 mm, the following procedure is adopted:the wire is advanced to the length of 4 000 mm and, in the case of adegree of stretching of 5%, is stretched by the amount of 200 mm.Subsequently, the wire is advanced once again by the amount of 2000 mmand is stretched once more by the amount of 100 mm. A wire portion witha length of 6000 mm, which has been stretched by the amount of 5%, hasthus been produced.

[0050] The method for producing a discontinuously stretched wire isdescribed below with reference to the stretching machine 21. Therolled-wire bundles 33.1 and 33.2 are provided on a double horizontalrun-off 34 for machining in the stretching machine 21. By the use of adouble horizontal run-off 34, for example, the end of the rolled-wirebundle 33.1 can be welded to the start of the rolled-wire bundle 33.2,so that work can be carried out without interruption. After the entirerolled-wire bundle 33.1 has been processed, a new rolled-wire bundle ispositioned on the run-off, and, if appropriate, its start is welded tothe end of the rolled-wire bundle 33.2. Wire portions can thus beproduced in large quantities continuously and without interruption.

[0051] The start of, for example, the rolled-wire bundle 33.1 isintroduced or shot into the stretching machine 21 and is prestraightenedin the roll-type straightening mill 22 in such a way that it becomeseasier for the wire 31 to be pushed through. The wire 31 is thereaftergripped by the first roll-type advancing unit 23 which follows theroll-type straightening mill 22. The first roll-type advancing unit 23consists of two oppositely directed rolls 35.1 and 35.2, between whichthe wire 31 is advanced, and of two drives 36.1 and 36.2 which drive therolls 35.1 and 35.2 in a controlled manner and are preferablycoordinated with one another. Instead of two separate drives 36.1 and36.2, only one drive may also drive both rolls 35.1 and 35.2, forexample via a gear. So that different wire diameters can be processed ina stretching machine 21 without any particular outlay, at least thelower or upper rolls of the roll-type straightening mill 22 and of thefirst roll-type advancing unit 23 are mounted displaceably in onedirection, for example in a vertical direction. The neutral position ofthe rolls corresponds to the smallest wire diameter to be processed (forexample, 4 mm), and the minimum latitude of movement of the displaceablerolls must correspond to the largest wire diameter to be processed (forexample, 12 mm). The setting of the interspace between the rolls may becarried out passively on the basis of the diameter of the pushed-in wire31 or actively by mechanical control. In a variant of this, the rollingsurfaces of the rolls may be coated with a deformable material whichallows the machining of the entire diameter range (for example, 4 mm to12 mm), without the rolls having to be displaced in one direction.

[0052] The wire 31 is advanced to the second clamping device 28 by meansof the roll-type advancing unit 23. The first clamping device 24 and thesecond clamping device 28 are constructed in essentially the same way.They have at least two clamping jaws 37.1, 37.2 and 38.1, 38.2 which aremoveable relative to one another and which clamp the wire 31 locatedbetween them. The clamping jaws 37.1, 37.2 and 38.1, 38.2 are movedmechanically or hydraulically in a controlled manner.

[0053] The first clamping device 24 is arranged on a hydraulic linearbooster 25 which can execute freely programmable travels. In thisexemplary embodiment, the stretching force generated by the linearbooster 25 amounts to about 70 kN and makes it possible to stretch awire having a diameter of 12 mm up to its maximum yield point of about630 N/mm². The wire 31 to be stretched is held by the first clampingdevice 24 and the second clamping device 28. Subsequently, the firstclamping device is moved, in the clamping state, opposite to the push-indirection by the amount of the desired degree of stretching. The frontpair of rolls 35.1 and 35.2 has to rotate opposite to the push-indirection of the wire 31 so that the stretching travel is compensated.The first stretched wire portion is produced in a start/stop operatingmode (stop-and-go). As soon as the values for this roll-wire bundle havebeen detected and stored, the production of the stretched wires takesplace. If differences in the measured final values are detected duringproduction, the said differences lying outside the defined tolerancerange, the force or the degree of stretching is adapted. At the sametime, stretched wires which do not conform to the desired requirementsor have material faults can be sorted out and removed from the furtherproduction process, for example in the production of structural-steelmats.

[0054] In the next work step, the stretched wire is transported furtheron by means of the first roll-type advancing unit 23. If two roll-typeadvancing units are arranged in a stretching machine, these arepreferably coordinated with one another (that is to say, synchronously)or operate actively or passively, depending on the position of the wire31.

[0055] Arranged at the second clamping device 28 is a cutting device 29which cuts the stretched wire 31 to the desired length, for example bymeans of a shear device.

[0056] In a further method for the industrial production ofdiscontinuously stretched wire, the stretching length for a wire portionis automatically adapted continuously on the basis of statisticevaluations of the stress/strain dependence. The statistic evaluation isbased on an average value which is prepared on the basis of a predefinednumber of, for example, fifty wire portions having measured and storedvalues. The automatic adaptation of the stretching length may in thiscase take place, for example, via the travel and/or the force. If thesteel quality changes or a new rolled wire is introduced into theapparatus, the machine is adapted automatically. By means of thismethod, operational documentation can be prepared from the production ofthe wire portions and may be used, for example, for operating-dataacquisition or for quality assurance.

[0057] In another method for the industrial production ofdiscontinuously stretched wire, the stretching length for a wire portionis related to a stress threshold value which defines the conclusion of apreflattening phase. In terms of the stress/strain diagram of the rolledwire, a value is defined as a control point on the elastic straight lineand ensures that the wire portion is absolutely straight. Such a stressthreshold value lies in the range of 200 N/mm² and 500 N/mm² in the caseof wire material which is used for the production of structural-steelmats and which conforms to the critical standards. First the wire isstretched. When the stress threshold value is reached, the end of the“gradation phase” is determined. A rolled wire delivered as a bundlemust first be oriented absolutely straight, so that stretching iscarried out in the required size and quality. As soon as the sensordetects that the wire is absolutely straight even at a lower value, ifappropriate the stress threshold value can be reduced for the subsequentwire portions. The advantage of this is that the number of cycles of theapparatus and therefore the quantity of stretched wire produced areincreased. When the stress threshold value is reached, the stretching ofthe wire portion, until the desired final value is reached, cancommence. The number of cycles of the apparatus according to theinvention is based on the cycle time for the production of a wireportion, which is composed of the advance of the wire portion, theclamping of the two clamping devices, the stretching stroke and theopening of the clamps and also the sum of the intermediate times. Themethod according to the invention makes it possible to havediscontinuous stretchings which, for example for a wire-portion lengthof 2000 mm, allow a number of cycles of 110 off/min (=3.66 m/s).

[0058] For a change of diameter, the wire 31 is drawn back completelyand the new wire is pushed or shot into the stretching machine 21. Owingto the described adaptable components of the individual devices, manualadaptations of the individual devices of the stretching machine can bedispensed with, thus appreciably increasing the productivity of thestretching machine, as compared with the prior art. The change ofdiameter can be automated by simple means.

[0059] A further possibility for increasing productivity is thearrangement of two units which are connected in parallel. The two unitscan be operated by means of only one hydraulic assembly.

[0060] The stretching machine 21 may be used both as a stand-alonesolution and as an integration in a plant for the production ofstructural-steel mats, the stretching machine preferably preceding theactual plant. That is to say, the wires stretched in the stretchingmachine are made available directly to the plant for the production ofstructural-steel mats and are taken over by the latter for furtherprocessing.

[0061] In conclusion, it must be stated that an apparatus and associatedmethods have been provided, which combine the stretching andstraightening operations and allow discontinuous stretching with anindustrially acceptable number of cycles, at the same time with qualitycontrol.

1. Apparatus for the industrial production of discontinuously stretchedwire (31), with two spaced-apart clamping devices (24 and 28), at leastone (24) of which is capable of being moved by the amount of astretching length, characterized in that at least one of the saidclamping devices (24 or 28) is equipped with a sensor for determiningthe wire stress.
 2. Apparatus according to claim 1, characterized inthat means for introducing or advancing the wire in the wirelongitudinal direction are provided.
 3. Apparatus according to claim 1,characterized in that it is provided on the entry side with a roll-typestraightening mill (22).
 4. Apparatus according to claim 3,characterized in that a first roll-type advancing unit (23), a firstclamping device (24), a straightening section (32) and a second clampingdevice (28) are arranged downstream of the roll-type straightening mill(22) in the direction of advance of the wire.
 5. Apparatus according toclaim 4, characterized in that a second roll-type advancing unit isarranged between the straightening section (32) and the second clampingdevice (28).
 6. Apparatus according to claim 4, characterized in thatthe first clamping device (24) is arranged on a linear hydraulic powerbooster (25).
 7. Apparatus according to claim 5, characterized in thatthe first clamping device (24) is arranged on a linear hydraulic powerbooster (25).
 8. Apparatus according to claim 1, characterized in that apressure cell is arranged as a sensor on the fixed clamping device (28).9. Apparatus according to claim 1, characterized in that it has on theexit side a cutting unit (29) for cutting the stretched wire (31) tolength.
 10. Apparatus according to claim 8, characterized in that it hason the exit side a receptacle for the intermediate storage of thecut-to-length stretched wire (31).
 11. Apparatus according to claim 1,characterized in that it comprises a control device which sets thestretching length on the basis of a measured wire stress.
 12. Plant witha wire-mesh welding machine and with a preceding apparatus (21) for theproduction of discontinuously stretched wire (31), with two spaced-apartclamping devices (24 and 28), at least one (24) of which is capable ofbeing moved by the amount of a stretching length, characterized in thatat least one of these is equipped with a sensor for determining the wirestress.
 13. Method for the industrial production of discontinuouslystretched wire, a wire portion (31) to be machined being gripped by twoclamping devices (24 and 28) and being stretched, characterized in that,by means of a sensor for measuring the wire stress and of a travelsensor, a stress/strain dependence is recorded, and in that the latteris stored, assigned to the wire portion, for further processing. 14.Method for the industrial production of discontinuously stretched wire,a wire portion (31) to be machined being gripped by two clamping devices(24 and 28) and being stretched, characterized in that, by means of asensor for measuring the wire stress and of a travel sensor, astress/strain dependence is recorded, and in that the stretching lengthis automatically adapted continuously on the basis of statisticevaluations of the stress/strain dependence.
 15. Method for theindustrial production of discontinuously stretched wire, a wire portion(31) to be machined being gripped by two clamping devices (24 and 28)and being stretched, characterized in that, by means of a sensor formeasuring the wire stress and of a travel sensor, a stress/straindependence is recorded, and in that the stretching length is related toa stress threshold value which defines the conclusion of a preflatteningphase.
 16. Method according to claim 15, characterized in that thestress threshold value is determined individually for each wire portion(31).
 17. Method according to one of claims 13 to 16, characterized inthat the wire (31) is introduced automatically in the wire longitudinaldirection and is cut to length automatically after stretching.